This invention relates to apparatus for manufacturing industrial diamonds.
Two known methods of making diamonds are disclosed in my U.S. Pat. No. 3,704,969. One of the early methods of making diamonds is shown in FIG. 2 of that patent, and involves the so-called "belt" method of making diamonds in which a charge was compressed between two dies. Unfortunately, however, because of the limited travel of the dies, and the further fact that the density of diamond is about 3.4, while that of graphite is only about 2.23, the limited travel of the two dies necessarily limited the amount of graphite which could be converted to diamond.
U.S. Pat. No. 4,119,708 disclosed an arrangement for use with a tungsten carbide piston which could have a longer travel, and greater compression of the charge. A hollow cylindrical bushing of salt is provided within a cylindrical opening in a tungsten carbide member, and a tungsten carbide piston is provided which has an outer diameter equal to the inner diameter of the opening in the tungsten carbide member forming the pressure vessel. The salt serves to insulate the central charge which is heated up by the flow of electricity through it. In the arrangement of U.S. Pat. No. 4,119,708, a plug of zinc is provided at the end of the charge so that, as the tungsten carbide piston is advanced, the zinc squeezes down into the inner diameter of the salt bushing and transmits the force of the piston to the charge within the bushing. By this technique, deformation of the salt bushing is avoided.
Unfortunately, the deformable member made of zinc does not always flow regularly or smoothly. In addition, the diameter of the tungsten carbide piston must be the full diameter of the opening in the tungsten carbide block, and such large diameter pistons are expensive, particularly with the frequent failure of tungsten carbide pistons at the high temperatures and pressures which are involved.
Accordingly, principal objects of the present invention are to reduce the diameter of the tungsten carbide piston which is employed for a given size charge, in the manufacturer of industrial diamonds, to improve control in the application of mechanical power to the charge, and to increase the dimensional stability of the process.